# Problem Two blocks of masses m1 andm2, with m1 &gt...

Problem Two blocks of masses m1 andm2, with m1 >m2, are placed in contact with each other on africtionless, horizontal surface, as in Active Figure 4.13a. Aconstant horizontal force = 118 N is applied to m1 asshown.

(a) If m1 = 15 kg and m2 = 10 kg, find themagnitude of the acceleration of the system of two blocks.

(b) Determine the magnitude of the contact force between thetwo blocks.

(c) Imagine that the force in Active Figure 4.13is applied toward the left on the right-hand block of massm2. Is the magnitude of the force 12 the sameas it was when the force was applied toward the right onm1?

1.  (a)
Assume F1  = 118 N   thenF1 = (m1 +m2) a
a = F1 / (m1 + m2) = 118 / (10 + 15) = 4.72m/s2
(b) let F2 = the force exerted on m2 by m1
we know a from (a) above so F2 = m2 a =10(4.72) = 47.2 N
(c) Now if we put the original force applied from the right weknow that a will be the same, i.e. 4.72 m/s2 . Sothe force exerted on m1 by m2 is
F3 = m1 a =15 (4.72) = 70.8 N
You can think of it as the mass "mediating" the effect of theforce. For instance assume you have a block of balsa woodnext to a refrigerator.  If you push on the refrigeratorit pushes against the balsa wood, but not as hard as if you push onthe balsa wood which pushes against the refrigerator.

2. a) a = F / (m1 + m2)

b) m1a = F1
m2a =F2

c)
F = m2a